Defluorination of hf alkylation reactor product



Jan. l5, 1963 F. T. sHl-:RK 3,073,877

DEFLUORINATION oF HF ALKYLATION REAcToR PRODUCT TO R EACTO R United States Patent ice 3,073,877 DEFLUORINATION F HF ALKYLATION REACTOR PRODUCT Fred T. Sherk, Bartlesville, Okla., assignerl to Phillips Petroleum Company, a corporation of Delaware Filed Apr. 5, 1960, Ser. No. 20,094 7 Claims. (Cl. 260-683.48)

This invention relates to the treatment of organic materials to remove therefrom fluorine-containing compounds. In one aspect this invention relates to an irn- Vproved method for removing ilumine-containing cornpounds from the hydrocarbon products of a hydrocarbon conversion process wherein anhydrous HF is used as a conversion catalyst. vIn another aspect this invention is concerned with a combination of related and cooperative steps whereby the process of .defluorination of the hydrocarbon is more completely and more eiciently performed.

In a process for the conversion of hydrocarbons wherein .anhydrous hydrogen fluoride (HF) is employed as a catalyst there inevitably occur side reactions in addition .to the desired conversion reaction. For example, hydrogen uoride reacts with some of the hydrocarbons to form organic fluorides. y

ln a typical HF alkylati-on reaction, for example, the alkyl-ation of isobutane with a butene to form isoctane, the reactor'eiiluent is fractionally distilled to remove lowboiling hydrocarbons from the alkylate. In those instances where the low-boiling hydrocarbons are recycled to the process or utilized as fuel, the presence therein of organic yil-uorides poses no problem. However, in those instances wherein the low-boiling hydrocarbons are utilized as a product, it is often necessary that ,these hydrocarbons be substantially free from hydrogenyuoride or organic iluorides.

yIt is therefore a principal object yof this invention to provide a method for removing ilumine-containing compounds from low-boiling hydrocarbons recovered from `an HF alkylation process. It is also an object of this invention to provide a method for removing iiuorine-containing compounds from products of HF alkylation and recovering resulting hydrogen iiuoridefor reuse in the process. Other objects and advantages will .become apparent to one skilled in .the art upon study of the disclosure, including vthe detailed description of the invention and the attached drawing wherein:

FIGURE `l is =a schematic flow sheet of an HF alkylation process having embodied therein the present invention;

.FIGURE 2 is -a more detailed schematic ow sheet of the steps which comprise the invention; and

FIGURE 3 illustrates a modication of the invention.

I have now discovered that organic iluorides can be substantially completely decomposed in a unitary process by a novel combination of integrated steps. Thus, according to this invention, a stream containing organic fluorides, e.g., .the overhead product from a fractional distillation step following the alkylation reaction, can be condensed so as to form a liquid hydrocarbon phase and a liquid vHF phase and a portion of the HF phase can be returned to the fractional distillation step to promote the decomposition of .theorganic uorides. I have found that the organic fluorine-containing compounds which are present in the feed to a distillation step following an HF alkylation reaction can be decomposed inthe distillation step in the presence of free HF. While the temperature conditions in the distillation column are usually sutiicient to promote this decomposition reaction, l prefer to pass the liquid HF from the phase separation to the feed to the distillation step at va point upstream 3,073,877 Patented Jan. 15, 1963 from the heater whichV is usually employed to raise the temperature of the feed to the distillation column to `a 'temperature in the range of about 130 to about 175 F. In this manner, the organic ilumine-containing compounds in the feed are intimately contacted with the HF at an elevated temperature so that the decomposition reaction is accelerated. There is no limiting upper ternperature and temperatures as high as 400 or 500 F., which sometimes are utilized in distillation operations, are applicable. l

yIn an HF `alkylation process wherein the irst fractional distillation step is for the purpose of removing .C3 and lighter materials overhead, this overhead stream will sometimes contain about 1000 to about 1200 p.p.m. of tiuorine in the form of fluorine-containing compounds such as alkyl fluorides. By utilization of this invention the fluorine-cont-aining compound content of this stream will be reduced to about 200 to about 300 ppm. The uoride content will also sometimes be as low as 200 to 300 ppm. .and the reduction in `fluoride content .by practice of the invention will be proportionately` as great as when ,the fluoride content is 1000 p.p.m. or greater. This reduction in ilumine-containing compounds is accomplished without changing the operating conditions of the alkylation process or of the fractional distillation steps which follow.

yIn the embodiment of FIGURE l, the alkylation reactants enter the system via c-onduit 11. These reactants comprise a paralin hydrocarbon having at `least one tertiary carbon atom per molecule and an alkylating agent such Vas an olen. For sake of simplicity in this description various valves, pumps and other auxiliary equipment will not be illustrated but `those skilled in the art will readily be able to supply these because the alkylation reaction is well known rin the art. Also for the sake of simplicity, the reaction will be described as applied to isobutane and butylene although it is to be understood that the reaction is not limited thereto. These reactants pass into reactor 13 where they are intimately mixed with hydroiluoric acid whichY enters via conduit .14. The reactor eilluent passes via conduit 15 to acid settler or separator 16 wherein the reaction efuent `is separated into an upper hydrocarbon phase and a lower acid phase. The hydrocarbon phase is passed through cond-uit 17 and heater 18 to fraction-ator 1 9 wherein a fractional ydistillation removes propane `and lighter products overhead via conduit 21 andcondenser 22 to accumulator 23 wherein a phasev yseparation occurs. The lighter hydrocarbon phase comprising propane and lighter materials is removed via conduit 24 and the heavier acid phase is removed via conduit 25 and passed via conduit 227 where it joins the reactor effluent hydrocarbons in conduit .17 Iand passes therewith through heat-k er 18 into fractionator 19. Excess HF acid over that required for recycle to vfractionator 19 lcontinues through conduit .26 and joins the acid in conduit 14, passing therewith into reactor 13. The kettle product from fractionator 19 is removed via conduit 28, a portion being returned to fractionator .1.9 via reboiler 29 and conduit 31. The material in conduit 28 is passed to fractionator 32 wherein isobutane is separated by fractional distillation and passed'overhead from fractionator 32 via conduit 33, condenser 33a, accumulator 33h and conduit 33C to conduit .'11 to be returned to reactor 13 as recycle'isobutane. The kettle product from ffractionator 32 passes via conduit 34 to fractionator 35. A portion ofthe ket tle .product is returned to fractionator `:t2 via reboiler 36 and .conduit 37. Normal butane is distilled from the materials in fractionator 35 and passes via conduit 3S and condenser 39 .to accumulator 41. Norm-a1 butane is removed from accumulator 41 via conduit 44. Alkyl# ate product is removed from fractionator 35 via conduit 45, a portion being returned via reboiler 46 and conduit 47 to fractionator 35.

Referring now to FIGURE 2 the reactor etiiuent passes to settler 16 via conduit 15 and a phase separation occurs in settler 16. Liquid HF is removed from the bottom of the settler. Liquid hydrocarbons are removed from the settler via conduit 17 and passed via pump 20, heater 18, and conduit 17a to fractionator 19 which is operated as a depropanizer, removing propane and lighter materials as overhead product via conduit 21 and condenser 22 to accumulator 23 wherein a phase separation occurs. Propane and lighter products are removed from the upper liquid layer via conduit 24 and liquid HF is removed from the lower liquid layer via conduit 25 and passed via conduit 27 to conduit 17 so as to be returned to fractionator 19. The kettle product comprising sub-v stantially uorine-free isobutane and heavier hydrocarbons is passed via conduit 2S to further separation steps as indicated in FIGURE l. The propane and lighter products are usually passed to an HF stripping step and a caustic soda wash step to remove residual HF. The HF removed can be recovered and returned to the alkylation reactor or otherwise utilized. Frequently the vapors from a stripping step containing propane and HF along with other materials if present are returned to conduit 21 and are fed to condenser 22 with the fractionator 19 overhead vapors. In such a case the HF phase removed from the accumulator 23 via conduit 25 contains all of the recovered free HF.

Typical operating conditions according to one installation of the invention are herewith described with reference to FIGURE 1, but it is to be understood that these operating conditions are exemplary and are not to be construed as unduly limiting the invention. Reactor 13 is operated at a temperature of 95 F. and 125 p.s.i.a. The acid rerun unit is operated to produce a liquid rerun acid containing some liquid isobutane and other hydrocarbons at a pressure and temperature similar t those given for the reactor. The hydrocarbon and acid materials are transported via conduit to the settler 16 where phase separation occurs at 95 F. The temperature of the feed to fractionator 19 is raised to 150 F. and fractionator 19 is operated at a pressure of 315 p.s.i., a bottom temperature of 215 F. and a top temperature of 136 F. Accumulator 23 is operated at 115 F. and 305 p.s.i.a. Fractionator 32 is operated at a pressure of 180 p.s.i.a., a bottom temperature of 340 F. and a top temperature of 150 F. Fractionator 35 is operated at a pressure of 85 p.s.i.a., a bottom temperature of 315 F., and a top temperature of 135 F. It is to be understood that a portion of the hydrocarbon vapors condensed and collected in the accumulator of each fractionator is returned to the top of the fractionator as reflux according to conventional practice.

In one typical HF alkylation installation, operated according to prior ait practices, the C3 and lighter product stream recovered as the overhead product from the fractionator corresponding to fractionator 19 of FIGURE 1 contained from 1000 to 1200 p.p.m. of fluorine in the form of fluorine-containing organic compounds after an HF stripping step and a caustic soda wash. When this installation was modiiied so as to operate according to the present invention, and HF was added to the fractionator feed in an amount of about 2 volume per cent of the feed, the uorine content of the C3 and lighter stream recovered as overhead product from the fractionator corresponding to fractionator 19 of FIGURE l after the HF stripping step and caustic soda wash was reduced to from 200 to 300 p.p.m.

In the process illustrated in FIGURE 1, the irst fractional distillation step is that of removing C3 and lighter hydrocarbons overhead and isobutane is removed as the overhead product in the second fractional distillation step. In some installations the irst fractional distillation step is a deisobutanizing step wherein the overhead product comprises isobutane as well as the C3 and lighter hydrocarbons, and C3 and lighter materials are removed overhead in a second fractional distillation step. In any event, the present invention is practiced on the iirst fractional distillation step and comprises condensing the fractionator overhead product, collecting the condensate in an accumulator wherein a phase separation occurs, and returning the acid phase, or at least a portion thereof, to the distillation step. In some installations, it may be desirable to divide the reactor eluent so that one portion passes to a depropanizer and a second portion passes to a deisobutanizer in which case tiuorine compounds would be present in the feed to each distillation step and the invention could be practiced on each or either distillation step.

FIGURE 3 illustrates a modification of the invention wherein the reactor effluent stream is divided between a depropanizer and a deisobutanizer. The stream in conduit 17 is divided so that a first portion of the stream passes via heater 1S and conduit 51 to depropanizer 52 and a second portion passes via conduits 53 and 54 to deisobutanizer 55. The overhead from depropanizer S2 passes via conduit V56 and condenser 57 to accumulator 58 where a phase separation occurs. Propane and lighter materials are removed via conduit 59. Liquid HF is removed from accumulator 53; the major portion is passed to conduit 17 via conduit 60, the remainder being passed to conduit 67 via conduit 60a. The kettle product from depropanizer 52 passes via conduit 61 to the feed conduit 54 of deisobutanizer 55. A portion of the depropanizer kettle product is diverted to reboiler 62 of depropanizer 52. If desired, a portion of the kettle product in conduit 61 can be diverted via conduit 61a. A heater 59 can be utilized in conduit 54 if desired.

The overhead product from deisobutanizer 55 passes via conduit 63 and condenser 64 to accumulator 65 where a phase separation occurs if the temperature is not too high. Isobutane recycle, containing some propane and normal butano, is removed via conduit 66 and recycled to the alkylation reactor. Liquid HF, if present, is removed via conduit 67 and is introduced into conduit 53 upstream from heater 50. The kettle product from deisobutanizer 55, comprising normal butane and alkylate, is passed 4via conduit 69 for further processing. A portion of this kettle product stream is diverted to reboiler 70 of deisobutanizer 55. The propane stream in conduit 59 and the alkylate stream in conduit 69 are substantially free of organic liuorides. The excess HF, over that required in fractionators 52 and 55, can be returned to the reactor via conduit 72.

The depropanizer kettle product in conduit 61 will usually be at a temperature of about 220 F. so that only a portion of this stream will be required to raise the temperature of the material in conduit 54 to the proper temperature, 130 to 175 F., and the remainder of this stream can be diverted to a point downstream, such as in conduit 61a. If desired, a heater such as heater 50 can be employed to raise the temperature of the material in conduit 54 and the kettle product can be utilized as the heat source. After the feed stream and the liquid HF have been in contact at a temperature in the range of 130-175" F. for a short time, the temperature can be raised to above this range.

With valves 81, 82, 83, 84, and 88 open, the HF -will ow through conduits 60a, 601:, 67, 72 and 73.

With valves 82 and 84 closed and valves 81, 83, 85 and '88 open, HF will tlow through conduits 60, 60a, 60h, 67 and 73.`

If desired, HF can be introduced into conduit `17 only, so that the feed to deisobutanizer 55 will be only partly treated. The alkylate in line 69 will be reduced in iiuorides less than if HF is introduced into conduit 53 to remove normal butane therefrom in another step,

as well as into conduit 17, but it may be economically desirable to operate in this manner.

I prefer to add the acid to the feed stream passing to the distillation step prior to the heating ot that stream so that the HF is in intimate contact with the disillation feed stream at the elevated temperature prior to passing to the distillation step; however, the HF can be added to other points in the distillation step to obtain satisfactory reduction yof iiuorine content of the product in substantially all cases, so long as there is present an excess of liquid HF, over that required for saturation or" the hydrocarbon, and an .alkylatable hydrocarbon.

The amount of HF required inthe feed t-o the distillation step is quite small, usually less than about 5 volume percent of the `feed stream, regardless of the amount of iiuorides present in the stream. Prefer-ably HF is added in an amount of about 1 to about 2 volume percent over the amount required to saturate the hydrocarbon at the conditions or temperature and pressure at the contacting of the HF `and hydrocarbon, although as much as 5 volume percent or more can be added.

Although the invention has been described as applied to the alkylation of a paraffin hydrocarbon, it is not to be construed as being limited to the alkylation of paraiiin` hydrocarbons but is equally applicable to the decomposition iof alkyl iiuorides derived from the alkylation of any alkylatable hydrocarbon such as aromatic hydrocarbons,

eg., benzene, and the like.

Reasonable variations and modiications are possible within the scope of this disclosure without departing from the spirit and scope of the invention.

That which is claimed is:

l. In the process of alkylating an alkylatable hydrocarbon with an alkylating agent in the presence of a hydrouoric `acid catalyst wherein the alkylation reaction eiiiuent separated from the hydrouoric acid catalyst and consisting essentially of hydrocarbons, containing organic tluorine compounds, is fractionally distilled stepwise to remove propane 4and lighter compounds in one step and the improvement comprising condensing the overhead products from the iirst distillation step; collecting the condensate so as fto form a liquid hydrocarbon phase and a liquid hydrofluoric :acid phase; removingthe hydrocarbon phase of reduced organic fluorine compound content; adding a stream consisting essentially of said hydrouoric acid phase to the feed to the first distillation step; heating the feed consisting essentially of liquidl hydrouoric acid and talkylation reaction eiiiuent hydrooarbons; and passing said heated mixture to said first distillation step.

2. In the process of alkylating a paraffin with an alkylating agent in the presence of a hydrofluoric acid catalyst wherein the reaction product, separated from the hydrofluoric acid catalyst and consisting essentially of organic uorine compounds along with other hydrocarf bons, is passed to a series of fractional distillation steps to recover alkyl-ate :and hydrocarbons lighter than alkylate, the improvement comprising condensing the overhead product from the first fraction-al distillation step; collecting the condensate so as to fonn a liquid hydrocarbon phase and a liquid hydrofluoric acid phase; removing the hydrocarbon phase of reduced organic fluorine kcompound content; removing the liquid hydrolluoric acid phase; passing at least a portion of the liquid hydrouoric acid phase into contact with the reaction product containing organic fluorine compounds; heating the resulting combined stream consisting essentially of liquid hydrouoric acid and the reaction product to a temperature in the range of about to 175 F.; passing the heated stream, as the sole feed, to :said rst fractional distillation step; and passing the kettle product from said rst fractional distillation step :to subsequent fractional distillation steps.

3. In the process of alkylating a paraffin with an aikylating agent inthe presence of a hydroiluoric acid catalyst wherein the reaction product containing the alkylate so produced, organic tluorine compounds and hydrocarbons lighter than the alkylate, is passed to a fractional distillation step, the improvement comprising condensing the overhead product from said fractional distillation; co1- lecting the condensate so as to form a liquid hydrocarbon phase and a liquid hydrofluoric acid phase; removing and recovering the hydrocarbon phase of reduced organic uonine compounds content; removing the hydrouoric acid phase; admixing at least about 0.5 volume percent, based on hydrocarbon, of said liquid acid with the reaction product passing to said distillation; passing remaining 'acid removed from said collectingstep lto the process of alkylating; heating the mixture consisting essentially of -acid and reaction product to a temperature in the range of about 130 to about 175 F.; passing 'the heated mixture as the sole feed to said fractional distillation step; and recovering the kettle product from said fractional distillation step.

4. The process of claim 3 wherein the alkylate and hydrocarbons lare passed to a depropanizing distillation step.

5. The process of claim 3 wherein the alkylate and hydrocarbons are passed to a deisobutanizing distillation step.

6. The process of claim 3 wherein the -alkylate and hydrocarbons are divided into two streams the first of which is passed to a depropanizing distillation step and the second of which is passed to a deisobutanizing distillation step.

7.- A process for removing organic ilumine-containing compounds from la hydrocarbon material containing same which comprises:

(l) passing a hydrocarbon material containing a minor quantity of an organic iiuonine-containing compound to a distillation step;

(2) condensing the overhead product from said distillation step to form `a liquid HF phase and a liquid hydrocarbon phase;

(3) recovering the liquid hydrocarbon phase as overhead product yof reduced organic ilumine-containing compound oon-tent;

(4) passing liquid HF from said liquid HF phase to the hydrocarbon material feed to the distillation step in au amount sutiicient to maintain an excess of liquid HF over that required to saturate the hydrocarbon material passing to said distillation step and heating the mixture consisting essentially of liquid HF and hydrocarbon material to -a temperature fin the range of about 130 to 175 F. prior to passage to said distillation step.

References Cited in the tile of this patent UNITED STATES PATENTS 2,372,338 Penisten Mar. 27, 1945 2,448,092 Gibson Aug. 31, 1948` 2,463,077 Zimmerman et al. Mar. 1, 1949 2,636,912 Leatherman Apr. 28, 1953 2,984,693 Cabbage May 16, 1961 

1. IN THE PROCESS OF ALKYLATING AN ALKYLATABLE HYDROCARBON WITH AN ALKYLATING AGENT IN THE PRESENCE OF A HYDROFLUORIC ACID CATALYST WHEREIN THE ALKYLATION REACTION EFFLUENT SEPARATED FROM THE HYDROFLUORIC ACID CATALYST AND CONSISTING ESSENTIALLY OF HYDROCARBONS, CONTAINING ORGANIC FLUORINE COMPOUNDS, IS FRACTIONALLY DISTILLED STEPWISE TO REMOVE PROPANE AND LIGHTER COMPOUNDS IN ONE STEP AND TO REMOVE NORMAL BUTANE THEREFROM IN ANOTHER STEP, THE IMPROVEMENT COMPRISING CONDENSING THE OVERHEAD PRODUCTS FROM THE FIRST DISTILLATION STEP; COLLECTING THE CONDENSATE SO AS TO FORM A LIQUID HYDROCARBON PHASE AND A LIQUID HYDROFLUORIC ACID PHASE; REMOVING THE HYDROCARBON PHASE OF REDUCED ORGANIC FLUORINE COMPOUND CONTENT; ADDING A STREAM CONSISTING ESSENTIALLY OF SAID HY- 